Filtration systems having a filter media for separating suspended solids from a liquid suspension such as a slurry may require the removal of the excess liquid from solid which has been separated from the slurry. One such system may be a coolant recovery system as for example of the type used in industrial machining operation wherein the coolant carrying the waste machine particles are processed to separate the coolant from the waste machine particles. The coolant is recovered and recycled into the machining operation. The separated waste particles after separation through a filter media may be in the form of a sludge. These sludges may present handling or disposal problems because of excessive quantities of liquid retained therein. In other liquid suspension filtration systems it may be desirable to recover the solid for further use rather than the liquid as described above. In such systems it may be desirable to remove the maximum quantity of liquid in order to minimize or eliminate drying of the separated suspended matter by the application of heat or the like. The recovery of coal fines of metallurgical coal resulting from coal washings is one such application in which it is desirable that the maximum quantity of the wash liquid be extracted from the fines in order that such fines may be suitable for use in metallurgical processes. In other liquid suspension filtration systems, it may be desirable to recover both the liquid and solid for further use.
In accordance with the present invention, it is proposed to provide a new and novel liquid suspension filtration method and apparatus for removing liquid from the suspended solids separated from liquid and deposited on a filter media or septum through which the liquid suspension carrying the solids has passed.
This is accomplished generally by introducing a liquid suspension into a pressure vessel having a filter wall section on which the solids are deposited. The vessel is filled so that the entire surface area of the filter section is covered. As the liquid flows through the filter wall section the suspended solid is deposited and accumulated thereon with the filtrate passing therethrough. When the solids accumulated on the filter section are of such a thickness that further filtration is no longer feasible, flow of liquid into the vessel is discontinued and pneumatic pressure means are actuated to create a pneumatic pressure within the vessel. This causes further flow of liquid through the accumulated solids on the filter section and gradually displaces the liquid suspension from the filter section to expose increasing areas of accumulated solid to the pneumatic pressure. The pneumatic pressure acting on the exposed solids is operative to compress or squeeze the solids against the filter section and remove additional liquid therefrom to form a layer in the nature of a cake. When the excess liquid is displaced from the filter section, the remaining liquid suspension is removed from the vessel and the pneumatic pressure is released. Thereafter the cake is removed from the septum and discharged from the vessel.
The above described arrangement is suitable for the extraction of liquids from suspended solids which are substantially air impervious when separated and deposited on the filter section. However, should the separated suspended solid not have the impervious characteristic, the arrangement of the present invention may be provided with a flexible fluid impervious curtain which overlies the filter section. The curtain is constructed and arranged so as to be spaced from the filter section to permit the passage of liquid through the latter. Upon the application of the pneumatic pressure to gradually displace the liquid from the filter section, the flexible curtain is forced into face to face engagement with the solids accumulated on the filter section by the pneumatic pressure acting thereon to compress the solids and extract liquid therefrom in substantially the same manner as described above.